add commit compare functionality

cmd/web.go

@@ -342,6 +342,7 @@ func runWeb(*cli.Context) {
 		r.Get("/commit/:branchname/*", repo.Diff)
 		r.Get("/releases", repo.Releases)
 		r.Get("/archive/*.*", repo.Download)
+		r.Get("/compare/:before([a-z0-9]+)...:after([a-z0-9]+)", repo.CompareDiff)
 	}, ignSignIn, middleware.RepoAssignment(true, true))
 
 	m.Group("/:username", func(r *macaron.Router) {